As known, many pourable food products, such as fruit juice, UHT (ultra-high-temperature treated) milk, wine, tomato sauce, etc., are sold in containers made of sterilized sheet packaging material.
A typical example of this type of container is the parallelepiped-shaped container for liquid or pourable food products known as Tetra Brik Aseptic (registered trademark), which is made by folding and sealing laminated sheet packaging material.
The packaging material has a multilayer structure substantially comprising a base layer for stiffness and strength, which may comprise a layer of fibrous material, e.g. paper, or mineral-filled polypropylene material, and a number of lamination layers of heat sealable plastic material, e.g. polyethylene films, covering both sides of the base layer.
In the case of aseptic containers for long-storage products, such as UHT milk, the packaging material also comprises a layer of gas-barrier material, e.g. aluminium foil or ethyl vinyl alcohol (EVOH) film, which is superimposed on a layer of heat-sealable plastic material, and is in turn covered with another layer of heat-sealable plastic material forming the inner face of the container eventually contacting the food product.
Containers of this sort are normally produced on fully automatic packaging machines, on which a continuous tube is formed from the web-fed packaging material. The web of packaging material is sterilized in the packaging machine. The web of packaging material so sterilized is then maintained in a closed, sterile environment, and is folded and sealed longitudinally to form a vertical tube.
The tube is filled with the sterilized or sterile-processed food product, and is sealed and subsequently cut along equally spaced cross sections to form pillow packs, which are then folded mechanically to form respective finished, e.g. substantially parallelepiped-shaped, containers.
Alternatively, the packaging material may be cut into blanks, which are formed into containers on forming spindles, and the containers are filled with the food product and sealed. One example of this type of container is the so-called “gable-top” container known by the trade name Tetra Rex (registered trademark).
To open the containers described above, various solutions have been proposed, including reclosable opening devices made of plastic material and substantially comprising a pouring spout, defining a through pouring opening and fitted to a wall of the container.
When producing the opening device, the opening of the pouring spout is sealed by a closing element connected integrally to the pouring spout and detachable from it along a smaller-section annular tearable membrane; the closing element extends at the same level as the packaging material so as to seal the hole in the wall of the container.
According to a known embodiment, the pouring spout and the closing element are injection molded in one piece directly on a through hole formed in the packaging material so as to seal it.
In particular, the portion of the packaging material provided with the hole on which the pouring spout and the closing element are to be formed is placed between two molds in an open configuration. The molds are then displaced towards the packaging material to reach a closed configuration, in which they cooperate with opposite faces of the packaging material and define a closed mold cavity housing the above-mentioned hole. The injection molding operation is performed by injecting the molten plastic material in the mold cavity defined by the molds in the closed configuration. More specifically, the molten plastic material is forced to fill completely the mold cavity so as to form the pouring spout and the closing element.
Subsequently, a lid is fitted to the pouring spout.
According to another known embodiment the pouring spout and the closing element are injection molded in one piece directly on a so-called “prelaminated” hole of the packaging material, i.e. a hole formed in the base layer only and covered by the other lamination layers, including the layer of gas-barrier material. The plastic material is injection molded on a first side of the “prelaminated” hole. The plastic material forms the closing portion on one side of the “prelaminated” hole and pierces the “prelaminated” hole along a circumferential region thereof, so forming a circumferential passage. The plastic material, therefore, flows through the circumferential passage and forms the pouring spout on a second side—opposite to the above-mentioned first side—of the “prelaminated” hole. After the molding operation, the lamination layers, in particular the layer of gas-barrier material, are integrated into the closing element and enhances the barrier properties, in particular the gas (oxygen) barrier properties, of the closing element.
A removable screw lid is fitted to the pouring spout to outwardly closing the latter and allowing closure of the container after the first opening by removing the closing element.
First opening of the package requires an unscrewing torque in an unscrewing direction, whilst re-closing of the package after first opening requires a screwing torque in a screwing direction, opposite to the unscrewing direction.
The unscrewing torque is greater than the screwing torque.
A drawback of the known opening devices is that if the user does not pay attention, he may apply a too high screwing torque—when re-closing the package—and so damage the opening device.
Another drawback of the known opening devices is that it may not be clear to the user which the unscrewing direction is. The user therefore, can unscrew the lid from the pouring spout by rotating the lid in the wrong direction and so break the opening device.
Another drawback of the known opening devices is that the user can pull the lid—instead of unscrewing them—and therefore damage the opening devices.